JP2007165155A - Radiation electron microscope for insulator sample observation using diagonally irradiating method of charged neutralization electron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique to obtain a clear electronic image without using an energy filter in which formed charge on a sample surface can be suppressed when an insulator sample installed on the sample board is observed in the field of a radiation electron microscope technology, and provide the radiation electron microscope applying it. <P>SOLUTION: In the method for observing the sample surface by irradiating excitation light onto the insulator sample installed on the sample board and by making photoelectron or secondary electron emitted from the sample surface form an image by a projection type electronic optical system, and in a state that a high electric field or high magnetic field is impressed on the sample face, so that the neutralization electron reflected or elastically scattered after having accomplished antistatic function can be removed by an angle restriction diaphragm (contrast aperture diaphragm) simultaneously with the excitation light, this is the method for observing the insulator sample surface on which charged neutralization electron beam is irradiated in a diagonal direction against the image forming optical axis by adjusting electro-optical conditions of a beam polarizer or a beam separator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a radiation electron microscope for observing an insulator sample using an oblique irradiation method of charged neutralized electrons.

The radiation electron microscope includes a method in which a strong electric field or a strong magnetic field is not applied on the sample surface and a method in which a strong electric field or a strong magnetic field is applied on the sample surface. If the former is a device that does not apply a strong electric field or a strong magnetic field on the sample surface, there is a method of irradiating the sample with a low-speed electron beam of about several eV to suppress charging of the insulator sample (for example, Patent Documents 1, 2).

In the latter case, a device that applies a strong electric field or a strong magnetic field on a sample surface is generally used by generating a rotationally symmetric electric field or magnetic field by an objective lens. There has been a method of suppressing charging of the insulating sample by irradiating the sample with a low-speed electron beam of about several eV along the rotationally symmetric electric field or the rotation center of the magnetic field. In addition, the electrons irradiated to the sample for suppressing charging are referred to as neutralizing electrons in the sense of neutralizing charging.

JP 2000-277048 A JP 2000-340160 A

However, in the latter case, there is a problem that the neutralized electrons irradiated on the sample are covered with a photoelectron image observed by reflection or elastic scattering. In general, in order to obtain a sufficient charge suppression effect, the sample is irradiated with neutralizing electrons having an intensity of several orders of magnitude or more with respect to the photoelectron intensity. This is because it becomes difficult to observe the photoelectron image. In order to solve this problem, it is necessary to incorporate an energy filter in the imaging electron optical system to remove the reflected or elastically scattered neutralized electrons.

The method and apparatus relating to the inventors' invention previously filed (Japanese Patent Application No. 2005-172859) are designed to suppress charging by irradiating neutralizing electrons in a state where a strong electric field or a strong magnetic field is applied to the surface of the insulator sample. By irradiating the sample with the neutralizing electron beam perpendicularly from the imaging optical axis, the neutralizing electron can reach the sample with sufficient intensity without being disturbed by the strong electric field or strong magnetic field. Was.

However, in this method, the neutralized electron beam reflected or elastically scattered by the sample and the photoelectron are imaged by drawing an electron trajectory having the same angle, so that the neutralized electron reflected or elastically scattered from the observed photoelectron image is removed. There is a problem that the configuration of the apparatus becomes complicated because it is necessary to remove it by using an energy filter or the like.

A radiant electron microscope typified by a photoelectron microscope is an electron microscope that obtains an enlarged image by drawing charged particles such as photoelectrons emitted from a sample placed on a sample stage with a strong electric field or a strong magnetic field. The present invention is a technique for suppressing the charging of the surface of a sample that occurs when an insulating sample placed on a sample stage is observed and obtaining a clear electronic image without using an energy filter. And a radiation electron microscope using it.

In the present invention, in order to remove the charged neutralized electrons reflected or elastically scattered from the sample without using an energy filter in the presence of a strong electric field or strong magnetic field on the surface of the insulator sample placed on the sample stage, the present invention neutralizes the charge neutralization. The electron beam is tilted slightly obliquely from the direction of the imaging optical axis that coincides with the rotationally symmetric electric field or magnetic field rotation center created by the objective lens (depending on the design of the electron optical system, when using an angle-limiting aperture of 400 μmφ The sample was irradiated at an angle (approximately 27 °) (hereinafter referred to as “oblique irradiation method” as appropriate).

That is, the present invention (1) irradiates an insulating sample placed on a sample stage with excitation light, forms photoelectrons or secondary electrons emitted from the sample surface with a projection electron optical system, and observes the sample surface In the method to perform, in the state where a strong electric field or a strong magnetic field is applied on the sample surface, simultaneously with the excitation light,
By adjusting the electron optical conditions of the beam deflector or beam separator, the charged neutralized electron beam is irradiated onto the sample surface obliquely with respect to the imaging optical axis, and the neutralized electrons reflected or elastically scattered from the sample surface are angled. This is a method for observing the surface of an insulator sample, which is characterized by removing with a limiting diaphragm (contrast diaphragm).

Also, (2) the method of observing the surface of an insulator sample according to (1) above, wherein the sample surface is irradiated with a light beam for suppressing charging simultaneously with the excitation light.

And (3) a sample stage on which an insulator sample is placed, a light source that emits excitation light, and an electron optical system that forms an image of photoelectrons and secondary electrons emitted from the sample surface. A charged neutralized electron beam having a function of suppressing charging of the sample with an electric field or strong magnetic field applied, or an ultraviolet light source for irradiating the sample surface with a light beam for suppressing charging A radiation deflector that irradiates the sample surface from a direction oblique to the imaging optical axis, and an angle limiting aperture (contrast aperture) installed in the imaging optical axis.

(4) The radiation electron microscope according to (3), further including a magnetic field electric field superposition type objective lens capable of adjusting a potential between the sample and the objective lens.

An image observed with a radiation electron microscope forms mainly photoelectrons or secondary electrons emitted in a direction perpendicular to the sample surface. On the other hand, when the charged neutralized electron beam is irradiated onto the sample surface from an oblique direction with respect to the imaging optical axis, the charged neutralized electrons cause a specular reflection on the sample and the same angle as the irradiation angle with respect to the vertical direction of the sample surface. Is reflected.

Here, by using an angle limiting diaphragm (contrast diaphragm) installed in the imaging optical axis, the neutralized electron beam having an angle is removed, so that weak photoelectrons or secondary electrons can be obtained without using an energy filter. High-intensity neutralized electrons can be separated, and a photoelectron or secondary electron image can be easily observed.

The conventional radiation electron microscope requires an energy filter for observation of the insulator and requires a very complicated device, but the oblique irradiation method of the present invention allows observation with a simple device that does not require the energy filter. enable.

FIG. 1 shows an example of the apparatus of the present invention. An excitation light source (X-ray source) 21 as a light source that is irradiated along the path 80 of the excitation light beam onto the surface of the insulator sample 11 placed on a sample stage (not shown);
An ultraviolet light source 22 that irradiates the surface of the sample 11 along the path 82 of the light beam for suppressing charging, and a neutralized electron beam source (electron gun) that irradiates the surface of the sample 11 along the path 81 of the neutralized electron beam. 31
Is attached to the basic optical system of the electron microscope.

The neutralizing electron beam can be irradiated to the surface of the sample 11 along the path (imaging optical axis) 90 of the imaging beam by the beam separator 61. A high negative voltage is applied to the sample 11.
X-rays and ultraviolet rays can be applied to the sample 11 at an angle, and electrons emitted from the sample 11 are converted into electron lens systems 41-51 (objective lens 41, magnetic lens 42 of a projection electron optical system).
, 43, 44, 45, projection electron optical system beam deflectors 46, 47, 48, 49, projection electron optical system stigmeters 50, 51), and CCD camera 7 via detector 71.
Observe at 2.

The neutralized electron beam emitted from the neutralized electron beam source 31 and irradiated along the path 81 of the neutralized electron beam is guided onto the imaging optical axis 90 using the beam separator 61 and is usually perpendicular to the sample 11. Therefore, it reaches the sample 11 without being disturbed by a strong electric field or magnetic field on the surface of the sample 11.

In order to neutralize the charging of the sample 11 using this neutralized electron beam, the potential of the electron gun 31 is shifted to the same value as the potential of the sample 11 or slightly to the negative polarity (depending on the shape and charging state of the sample). 1 to
Set to a value of about 5 eV. By doing so, when the surface of the sample 11 is in a neutral state before charging, the irradiation energy of the neutralized electron beam to the sample 11 is approximately 0 eV, and the irradiated electrons are repelled by the surface potential of the sample 11. Thus, the light is reflected without hitting the surface of the sample 11. Thus, the electrons reflected by the surface potential of the sample 11 are called reflected electrons.

When the sample 11 is irradiated with X-rays or ultraviolet rays to emit photoelectrons or secondary electrons and the sample 11 is positively charged, a difference occurs between the potential of the electron gun 31 and the potential of the sample 11. When this potential difference occurs, the irradiated neutralized electron beam starts to strike the surface of the sample 11 with the kinetic energy of the potential difference, and the charge generated on the surface of the sample 11 is neutralized.

When the charge on the surface of the sample 11 is neutralized, the potential of the sample 11 returns to its original state, and incident electrons are reflected again immediately before the surface of the sample 11. In this way, neutralization is completed when the potential of the sample 11 is balanced.

At this time, if a neutralized electron beam is irradiated perpendicularly to the surface of the sample 11, a problem occurs in which reflected electrons and elastically scattered electrons are covered with a photoelectron image to be observed (see FIG. 2A). Fig. 2 (a)
Is the electron trajectory 110-112 of the imaging photoelectrons that the photoelectrons emitted from the sample 11 draw for imaging on the image plane 100 via the objective lens 41.

FIG. 2B shows an electron trajectory 11 of a neutralized electron beam irradiated from an oblique direction with respect to the imaging optical axis.
3 is indicated by a solid line. Only neutralized electrons reflected or elastically scattered by the sample 11 can be removed by the angle limiting aperture CA. A dotted line is the electron orbit of the imaging photoelectron shown in (a). The angle limiting diaphragm is a component generally called a “diffraction diaphragm” in a transmission electron microscope (TEM), and is also called a “contrast diaphragm”. In the present invention, in order to limit the angle of the emitted photoelectron or secondary electron, it is described as “angle limit stop”.

In general, in order to obtain a sufficient charge suppression effect, the sample is irradiated with neutralization electrons having an intensity of several orders of magnitude or more with respect to the photoelectron intensity.
It is virtually impossible to observe the photoelectron image.

Conventionally, in order to remove the reflected electrons, an energy filter is built in the imaging electron optical system, and the surface is observed by selecting and imaging photoelectrons using the energy filter.

On the other hand, in the present invention, as shown in FIG. 2B, the beam is deflected greatly by using the beam deflector 35 of the electron gun 31 and the beam is returned by using the beam separator 61. By adjusting the conditions, the neutralized electron beam is slightly shifted from the vertical direction with respect to the surface of the sample 11 and obliquely (depending on the design of the electron optical system, approximately 27 ° when an angle-limiting aperture having a diameter of 400 μm is used. ) By irradiation, the neutralized electrons after fulfilling the charge suppressing function are reflected or elastically scattered in the specular reflection direction with respect to the irradiation direction.

Since neutralization electrons after fulfilling the charge suppressing function reflected or elastically scattered in the specular reflection direction have an angle with respect to the imaging optical axis (perpendicular to the surface of the sample), FIG. ), It can be removed by using an angle limiting diaphragm (contrast diaphragm: CA), and a photoelectron image emitted by X-rays can be easily observed without an energy filter.

Among the electron microscopes, photoelectron microscope devices that use photoelectrons for imaging in particular have begun to be industrially used as chemical state analyzers with high spatial resolution. Accordingly, the fact that the oblique irradiation method of the present invention makes it possible to easily observe an insulator with a photoelectron microscope device contributes to industrial use and brings an economic effect.

Schematic schematic diagram of a radiation electron microscope. The schematic diagram which shows the relationship between the electron orbit of the imaging photoelectron discharge | released from the sample, and the electron orbit of a neutralization electron.

Explanation of symbols

11: Sample 21: Excitation light source 22: Ultraviolet light source 31: Neutralization electron beam source 32, 33: Magnetic lens 34 of neutralization electron beam system, 35: Beam deflector 36 of neutralization electron beam system: Neutralization electron beam system Stigmator 41: objective lenses 42, 43, 44, 45: magnetic lenses 46, 47, 48, 49 of projection type electron optical system: beam deflector 50.51: of projection type electron optical system Stigmeter 61: Beam separator 71: Detector 72: CCD camera 80: Excitation light beam path 81: Neutralization electron beam path 82: Charge suppression light beam path 90: Imaging beam path 100: Image plane 110 , 111, 112: Electron trajectory of imaging photoelectrons 113: Electron trajectory of neutralizing electron beam CA: Angle limiting aperture (contrast aperture / diffraction aperture)

Claims (4)

In the method of observing a sample surface by irradiating an insulating sample placed on a sample stage with excitation light and forming an image of photoelectrons or secondary electrons emitted from the sample surface with a projection electron optical system, While charging an electric field or strong magnetic field, charging is performed so that neutralization electrons reflected or elastically scattered on the sample surface after performing the charge suppression function simultaneously with the excitation light can be removed with an angle limiting diaphragm (contrast diaphragm) A method of observing an insulator sample surface, wherein the sample surface is irradiated with a sum electron beam from an oblique direction with respect to an imaging optical axis by adjusting an electron optical condition of a beam deflector or a beam separator. 2. The method of observing an insulator sample surface according to claim 1, wherein the sample surface is irradiated with a light beam for suppressing charging simultaneously with the excitation light. It has a sample stage on which an insulator sample is placed, a light source that emits excitation light, and an electron optical system that images photoelectrons and secondary electrons emitted from the sample surface. A strong electric field or strong magnetic field is generated on the sample surface. A charged neutralization electron beam source having a function of suppressing charging of the sample in an applied state or an ultraviolet light source that irradiates the sample surface with a light beam for suppressing charging, and the charged neutralizing electron beam is applied to the imaging optical axis. A radiation electron microscope comprising: a beam deflector that irradiates the sample surface obliquely with respect to the angle; and an angle limiting diaphragm (contrast diaphragm) installed in the imaging optical axis. 4. A radiation electron microscope according to claim 3, further comprising a magnetic field electric field superposition type objective lens capable of adjusting a potential between the sample and the objective lens.

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